https://thefactsource.com/concrete-arrows-in-american-desert-airmail-beacons/
Horse express, railroad mail, and finally airmail
The vast distance between America’s Atlantic and Pacific coast was covered first by horse-mounted riders relaying the mail. The 1860 Pony Express was advertised to take only 10 days from coast to coast. This time was decreased by railroad in late 1800s.
But introduction of airmail changed everything. Airplanes were much faster than railroad, but still relatively slow back in 1920s. Airco DH.4 was a typical airmail machine, and its maximum speed was 143 mph (230 km/h). Airplanes could travel only in daylight. These were times long before GPS and satellite navigation. It was only 20 years after Wright Brothers’ maiden flight, but aircraft were already commonly used for mail delivery.
